Tunable MIM plasmonic near-infrared transmissive metasurface

Metasurfaces are engineered surfaces consisting of deep subwavelength artificial structures that enables full control of the electromagnetic waves. Metasurfaces are not only being used in many applications from microwave to... [ view full abstract ]

Metasurfaces are engineered surfaces consisting of deep subwavelength artificial structures that enables full control of the electromagnetic waves. Metasurfaces are not only being used in many applications from microwave to optics but also paving the way to many new exciting applications such as programmable on-demand optics and photonics in the near future. Active control of light absorption in the near-infrared spectrum has very practical and fundamental significance. Although different mechanisms and materials including graphene [1] and ITO [2] has been used to design such tunable metasurfaces, they have mostly been reflection type, at longer wavelength up to middle-infrared, and very sensitive to light polarization. Here, we demonstrate an MIM plasmonic transmissive light modulator metasurface in the near-infrared spectrum.

Each unit cell includes circular MIM structure (radius=530 nm) with 70 nm thick Aluminum on top and bottom and 60 nm thick SiO₂ as an insulator and 6 nm thick ITO as the tunable material between top Al and SiO₂ insulator (Figure 1). Each unit cell is 800 nm square with 30 nm thick beam (DC connection) attached to both sides of each circular resonator. ITO, a transparent conductive oxide, is modeled using Drude model with the plasma frequency ω_p0=8.24×10¹⁴ rad/s [3]. The refractive index has the highest change in the wavelength range of 1500-2000 nm when the plasma frequency is increased to ω_p1=2.55×10¹⁵ rad/s [3] after applying DC voltage (Figure 2), while the extinction coefficient is increased as a result. The transmission coefficient is increased from ⁓0% to 20% at the wavelength of 1650 nm while the reflection coefficient is dropped from 66% to 48% (Figure 3). The transmission coefficient drops 50% from 65% to 15% at 1820 nm while the reflection coefficient increases from 0% to 22%.

Here we demonstrate a tunable transmissive metasurface using ITO films in the MIM resonators. The performance of the metasurface is shown using FDTD simulations. The operational frequency of the metasurface could be easily altered by changing the radius of resonators and ITO film properties during the fabrication process.

[1] 10.1021/ph5003279

[2] 10.1021/acs.nanolett.6b00555

[3] 10.1364/OL.42.000005